1. Stageberg, F.E., Cantor, R., Goldman, A.M., Arnold, G.B.: J. Low Temp. Phys. 60 (1985) 437.
2. Yanson, I.K., Balkaskin, O.P., Krasnogorov, A.Y.: Zh. Eksp. Teor. Fiz. Pis'ma Red. 23 (1976) 458.
3. Wei, Chong-De, Luo, Xiao-Lan, Meng, Xao-Fan: Acta Phys. Sin. 31 (1982) 699.
4. Wong, L., Shih, S., Tomasch, W.J.: Phys. Rev. B23 (1981) 5775.
5. Henkels, W.H., Kircher, C.J.: IEEE Trans. Magn., MAG-13 (1977) 63.